The present invention relates to the field of micromechanisms. Particularly this invention pertains to the fabrication of 3-dimensional micromechanisms such as micromanipulators, microfluidic valves, actuators and end effectors for milli- and micro-robotic applications, precision data head manipulator for high density data storage, positioners for microphotonic systems, and other systems used in the field of micromechanisms.
More particularly, the present invention relates to a fabrication process for creating 3-dimensional micromechanisms in parallel fashion without need for post processing assembly.
Further, the present invention relates to the fabrication of 3-dimensional micromechanisms in which respective portions of a 3-dimensional micromechanism are created in separate wafers which are bonded together in sequence to form a final product (3-dimensional micromechanism) which may include variety of structural elements, such as: actuators, platforms, links, embedded joints coupled between the structural elements of the 3-dimensional micromechanisms such as linear sliders, ball-in-socket structures, overhanging or enclosed components, as well as other elements useful in this field.
Furthermore, the present invention relates to the fabrication of 3-dimensional micromechanisms based on thermally grown SiO2 as a material for structural elements of the micromechanisms.
As the miniaturization technology of complex engineering systems accelerates, the need for high-precision micromechanisms is becoming increasingly evident. For example, NASA predicts that the next generation of miniaturized spacecrafts will require micro-scale mechanisms for the deployment and manipulation of structures such as antennas, solar sails, and telescopes.
Such small-scale mechanisms will require dramatic reductions in size and weight over current technology. Typically, a Micro Electro Mechanical System (MEMS), such as a three-degree-of-freedom silicon-based platform manipulator, employs a combination of prismatic and pseudo-revolute kinematic pairs to achieve functionality. Micromanipulators include a moving platform, operatively connected to actuators through respective links. The moving platform and the actuators are coupled to the links through different joints. The controlled movement of the actuators is conveyed through the links to the moving platform and thus drives the platform in a predetermined direction through a predetermined distance. The dimensions of such a micromanipulator ranges from several microns to thousands of microns.
Silicon-based micromechanisms are manufactured using a variety of manufacturing techniques. Many of these technologies, such as LIGA, DRIE (deep reactive ion etching), and laser etching, result in simple extrusions of 2-dimensional planar structures. Some methods which are capable of generating true 3-dimensional microstructures, such as component bonding and hinged structure fabrication, require manual assembly and are not well suited for low-cost, mass-produced micromechanisms. Techniques such as micro stereo lithography and focused laser/ion beam deposition are not parallel processes and thus are not cost-effective technologies. In addition, many of these techniques, such as hinged structure fabrication, rely on thin film technology. and thus cannot produce mechanically-robust mechanisms capable of interfacing with macro-scale forces.
Existing 3-D micromachined structures may be loosely categorized as belonging to one of three groups: serially-processed microstructures, assembled microstructures, and parallel-processed microstructures.
Serially-processed microstructures, produced by techniques such as laser or focused ion beam etching and deposition, have been developed by leveraging from existing technologies used for performing modifications and corrections to fabricated VLSI (very large scale integration) circuits. Gas-assisted laser etching techniques used for high-aspect-ratio milling, and localized ion-beam-induced deposition has been demonstrated viable for 3D micromechanical structures. Other serial techniques based on non-IC processing have also been successfully used. As an example, stereo lithography systems, commercially applied to macro-scale desktop prototyping has recently been adapted to the microfabrication of polymer and plated metal structures with dimensions as low as 5 xcexcm.
While these techniques offer significant design flexibility for producing arbitrary 3-D shapes on the microscale level, they must be fabricated one device at a time resulting in high manufacturing costs and limiting their application for mass-produced devices. Additionally, the range of dimensions (both in-plane and out-of-plane) which can be achieved by these techniques are limited by relatively slow processing speeds.
Assembled microstructures which employ parallel fabrication processes to form mechanical components to be later hand-assembled, have been successfully demonstrated. Simple pick-and-place of high-aspect-ratio electroplated microcomponents produced by LIGA methods has been used to produce a variety of 3-D structures with large x-y-z dimensional range. Bonding methods provide additional flexibility by allowing selected components to be xe2x80x9cweldedxe2x80x9d into place after assembly. Hinged structures have proven very successful for a variety of applications.
An important capability of assembly processes is the potential for producing freestanding structures such as hub-and-axle assemblies. However, due to the nature of the assembly process, they cannot achieve complex structures such as ball-and-socket devices. Additionally, these methods require meticulous hand assembly of individual components, and as such are not considered truly parallel processes. The additional costs required for final assembly of these 3-D structures makes them prohibitively expensive for most applications.
Parallel processes offer great potential for low cost, mass-produced microstructures with 3-D geometries. Bulk-etched silicon devices fabricated using isotropic and anisotropic wet etchants together with etch-stop techniques have been thoroughly explored over in recent times. Bulk-etching techniques are capable of producing devices with large dimensional ranges, both in- and out-of the wafer plane, but are extremely limited in the types of geometries which can be achieved. Fabrication techniques capable of producing high-aspect-ratio structures, such as LIGA and deep-RIE of silicon are capable of generating arbitrary in-plane geometries however, out-of-plane dimensions are limited to simple extrusions of the in-plane structures.
Thus although significant progress has been made in fabrication of planar micromachined mechanisms, current manufacturing technology still results in fragile structures which cannot survive typical macro-scale loading conditions. There remains a strong need for fabrication technology capable of producing fully 3-dimensional micromechanisms which are mechanically robust enough to couple macro-scale forces and disturbances with precise micro-scale motions.
The ability to produce true 3-dimensional micromechanisms in a parallel fabrication technology while eliminating the post-processing assembly is a long standing need in the art.
It is, therefore, an object of the present invention to provide a fully parallel process which permits production of true 3-dimensional micromechanisms of nearly arbitrary in plane and out-of-plane shapes.
It is another object of the present invention to provide a process for 3-dimensional microstructures manufacturing which does not need a post-processing assembly, thus enabling the development of extremely complex 3-D micromechanisms in a relatively low-cost, high volume and less time consuming fashion.
It is a further object of the present invention to provide parallel microfabrication technology for producing silicon based 3-dimensional Micro-Electro-Mechanical Systems (3DMEMS""s) capable of achieving out-of-wafer dimensions much larger than traditional surface micromachined structures. This concept permits the manufacture of arbitrary planar shapes and kinematic pairs, such as linear sliders (e.g., pistons), ball-in-socket structures, and similar overhanging or enclosed components.
It is still another object of the present invention to provide a 3-D MEMS fabrication process which allows for the integration of both VLSI circuitry and traditional surface-micromachined devices without resorting to two-chip solutions such as solder bump attach or multi-chip modules.
It is a further object of the present invention to provide a fabrication process for manufacturing of mechanically-robust 3-D micromechanisms, microfluidic components, actuators and end-effectors for milli- and micro-robotic applications, precision data head manipulation for high density data storage, and positioners for microphotonic systems capable of large displacements and precise motion in three dimensions.
The 3-dimensional Micro Electro Mechanical system (3DMEMS) manufacturing process, is a novel technique for the fabrication of true 3-dimensional microstructures. It is a fully parallel microfabrication process which is compatible with backend processing for both CMOS fabrication and polysilicon micromachining. The fabrication technique of the present invention permits a low-cost mass-production of truly 3-dimensional MicroElectroMechanical systems (MEMS) components with planar dimensions as small as 4 xcexcm, and out-of-plane dimensions ranging from approximately 5 microns to several thousand microns. The 3DMEMS process allows for the production of mechanically-robust, multi-level devices with partially and fully enclosed components, such as ball joints and pistons, in a parallel fabrication flow. Additionally, the technology supports the integration of CMOS circuitry and traditional polysilicon MEMS structures at the top level of the mechanisms, resulting in complete 3-dimensional Microsystems.
In accordance with the teachings of the present invention, the 3DMEMS process employs several micromachining techniques, including the use of silicon-on-insulator (SOI) substrate wafers, deep reactive ion etching. (DRIE) of bulk silicon, chemical-mechanical polishing (CMP) of silicon wafer surfaces, silicon wafer bonding, and xenon difluoride (XeF2) gas-phase silicon etching.
The 3-dimensional structures are produced in successive layers, wherein in each layer a respective portion of a 3-D micromechanism is created to be further fusion bonded to other portions of the 3-D micromechanism formed in other layers. In this manner, in a first SOI wafer layer, a respective structural element of the 3-D micromechanism is made by defining this portion by the SiO2 which is thermally grown in channels etched via DRIE in the SOI substrate. When the oxidation of this first layer is complete, the surface is smoothed by CMP (chemical-mechanical polishing), and a next SOI wafer is hydrophobically bonded to the newly smoothed surface. This new substrate wafer is thinned to the desired thickness by another CMP step, and the next layer is etched via DRIE to make the next structural element of the 3-D micromechanism. Substantially thermal oxidation is performed to contour the next structural element of the 3-D micromechanism by SiO2.
When all the layers have been processed, backend CMOS fabrication and surface micromachining may be performed, followed by photoresist passivation and XeF2 etching to remove the exposed silicon which leaves the desired SiO2 blocks and selected silicon structures.
While this technique is conceptually simple, a variety of extremely complicated 3-dimensional structures may be produced in this manner. For example, devices which can be fabricated include planar, revolute, and spherical joints, gear-and-cog systems with combined vertical and horizontal rotational axes, and passageways (cylinders) with enclosed pistons for hydraulic or pneumatic actuation, as well as other elements useful in this field.